Technical Field
The present disclosure relates to visualization of three-dimensional (3-D) data and, more specifically, to techniques for visualization of 3-D ground-penetrating radar (GPR) data or other types of subsurface 3-D data.
Background Information
GPR is a technology that uses radar pulses to collect data deceptive of features below the surface of a material (subsurface features). Most often, the material is the ground, however in certain applications, the material may be concrete, steel, or some other material, or combinations of materials, located above ground level. In a typical GPR system, high-frequency radio waves (e.g., in the ultra high frequency (UHF) or very high frequency (VHF) bands) are generated and transmitted into the material. The waves travel through the material, and when they reach a boundary between two regions with different dielectric constants, a portion of the waves is reflected back. The boundaries between dielectric constants typically coincide with boundaries of objects disposed in the material, voids in the material, changes in composition of the material, or other features. The reflected waves are typically detected by an antenna of the GPR system, arranged on the surface. The GPR system measures variations in the reflected waves, and such variations are used to generate GPR data descriptive of subsurface features. While the GPR data may be used for different purposes, it is most often used to produce an image of the subsurface features. Depending on factors such as material type, density, and the presence of certain interfering substances, the quality of GPR data may vary. However, for many exploratory applications, even low quality GPR data is quite useful, as it provides the user with an indication of what lies below the surface prior to disturbing the material (e.g., digging in the ground).
Early GPR systems typically utilized a two-dimensional (2-D) scanning methodology and produced 2-D GPR data. From the 2-D GPR data, a 2-D image could be generated. More recent GPR systems may utilize a 3-D scanning methodology. In one type of 3-D scanning methodology, the GPR system transmits and receives back reflected waves at a series of locations along the surface, to collect GPR data corresponding to a series of 2-D vertical profiles through the material. The GPR data corresponding to the vertical profiles is assembled in order, for example, in a data matrix, to produce a collection of data that describes subsurface features in three dimensions (3-D GPR data). The 3-D GPR data may be used to produce tomographic images. In typical tomographic images, the 3-D GPR data is “sliced” (e.g., horizontally) to create a series of 2-D images that show subsurface features as they appear at various intervals (e.g., depths).
While topographic images produced from 3-D GPR data may be useful in many applications, they suffer shortcomings. The images are generally presented to a user in a purely virtual context, disconnected from the physical world. For example, they may be displayed in isolation in the user interface of a software application on the display screen of a computer. The images are not visually correlated with the physical world. In order to understand size and location of subsurface features that may be shown in the images, the user may have to take measurements in the displayed images, scale them to physical world dimensions, and then attempt to correlate these with landmarks on the surface in the physical world. Often the user may attempt to mark out the features on the surface, for example, with paint, to try and understand them. This process may be time consuming and error prone. If mistakes are made, the benefits of the 3-D GPR data may be lost. The 3-D GPR data, rather than provide an indication of what lies below the surface, may actually mislead the user, causing them to believe something is located where it is not.